1. Field of the Invention
The present general inventive concept relates to an audio encoding and/or decoding apparatus and method, and particularly, to an adaptive time/frequency-based audio encoding apparatus and a method of determining an encoding mode of the apparatus, in which time-based encoding or frequency-based encoding is adaptively applied according to a data property, thereby acquiring high compression efficiency with the use of a coding advantage of the time-based and frequency-based encoding modes.
2. Description of the Related Art
Conventional voice/audio compression modes are largely classified into two types. One type is audio codec and the other type is voice codec. The audio codec, such as aacPlus, is an algorithm to compress a signal in a frequency domain, to which a psychoacoustic model is applied. When the audio codec is used to compress a voice signal instead of an audio signal, timbre is deteriorated much more than if the voice signal was compressed with the voice codec mode, even if a same amount of data is encoded. Particularly, there is greater timbre deterioration around a frequency of an attack signal. On the other hand, the voice codec such as AMR-WB is an algorithm to compress a signal in a time domain. When the voice codec is used to compress an audio signal instead of a voice signal, timbre is deteriorated much more than if the audio signal was compressed with audio codec mode, even if a same amount of data is encoded.
Considering the aforementioned conventional problems with the voice/audio compression modes, there has been provided an Adaptive Multi-Rate Wideband codec (AMR-WB)+mode (3GPP TS 26,290) as a conventional technology to efficiently perform voice/audio compression simultaneously. In the AMR-WB+mode (3GPP TS 26,290), Algebraic Code Excited Linear Prediction (ACELP) is used to compress a voice, and Transform Coded Excitation (TCX) is used to compress an audio. The AMR-WB+ mode (3GPP TS 26,290) determines whether to apply the ACELP mode or the TCX mode to encode, for each frame. Particularly, the AMR-WB+ mode (3GPP TS 26,290) operates efficiently when compressing an object similar to a voice signal. However, deterioration of timbre or a compression ratio, caused by an encoding process for each frame, occurs when the object to be compressed is similar to an audio signal.
Accordingly, when input audio data is encoded by selectively applying an encoding mode, an encoding mode determination as well as standards associated with the encoding mode determination are very important factors which have a great effect on encoding performance.